The Demon Inside
by SherlockDW2013
Summary: A young girl is taken over by a demon, so her best friend, The Winchester brothers, Castiel, Sherlock Holmes, John Watson and Greg Lestrade need to get it out. To make things worse, they only have a week to do it. And the clock is ticking. Rated for Strong Language and Blood.
1. Finding Out

UK knew something was wrong the moment she saw Kassey this morning. There was just something _off_. She would know because Kassey and she were like sisters. So if there wasn't something right with one of them, the other would know.

So when UK decided to confront Kassey, she didn't expect her to start hissing wildly, her eyes to turn _black_ and start to climb up a wall _or_3 men -who were called Dean, Sam and Castiel- to come out of nowhere with exorcising equipment.

"Leave the girl's body!" Dean growled, obviously sick with what was happening –or what used to be her. She just hissed, spittle flying from her lips

"Never!" she began to climb up further on the wall. Dean pulled out a gun but UK grabbed a hold of his arm

"NO! You'll harm Kassey!"

Sam began to perform the exorcism but Kassey noticed. She spat on him, interrupting the exorcism. The demon laughed before climbing out of the nearby open window

"KASSEY! NO! Come back!" UK shouted in desperation before crumbling to her knees and sobbing. Sam looked to UK with pity.

Out of nowhere a bunch of police cars pull up and Sherlock Holmes, Lestrade and John Watson emerge from the vehicle and enter the house. Lestrade looked between Dean, Sam and Castiel with curiosity before his eyes caught onto UK

"What's going on?" UK just sobbed harder

"Kassey!" Lestrade kneeled beside UK

"What happened?" he said gently

She takes in a haggard breath trying to grow up.

"S-she was possessed... I-I don't believe in that sort of thing but I know w-what I saw!"  
The moment the word 'possessed' left her mouth, John frowned

"Possessed?" he asked. UK nods.

"I saw a show about it... her eyes turned black."

"Black?" John shakes his head and looks to Sherlock "Sherlock is this even possible? ... Sherlock?" Sherlock was busy observing everyone.

"She... Climbed up the wall... What? And the smell of sulphur..." He muttered

"Sulphur?" John and Lestrade frowned.

"Just who are you 3?" Lestrade turns and faces Castiel, Dean and Sam. Castiel quickly poofs away, leaving Sam and Dean to stand there awkwardly.

"Where the hell did that guy go?!" Lestrade exclaims and indicates the space which Castiel previously occupied. Castiel appears behind Lestrade.

"Here." said he plainly

"Jesus!" Lestrade practically squeals and topples back into John. Causing both men to go sprawling across the floor. UK notices Dean and Sam's attempt to conceal their laughs

"All of you Shut Up!" Sherlock growls suddenly and all heads turn to him.

"Yes, Mr Grumpy?" Dean said and crossed his arms. Sherlock grips at his hair and squeezes his eyes shut

"'S'up with him?" Dean says to John

"Either he's in pain -which I doubt- or he's trying to think." John replies as he scrapes the dirt and dust off himself. Sherlock whirls

"Anderson you're putting me off!" Sherlock hissed to the forensic scientist who had just entered through the door

"But he didn't even say anything!" Dean protested.

"He was thinking. It annoys me!" snapped Sherlock

"You can read minds?!" Sherlock eyes him and sighed

"Dear God, I feel sorry for your miniscule brains..."

"No one knows." John leaned in and answered Deans question.

"Shut up!" Sherlock snarled again. "Anderson, turn around!"

"Do it!" Lestrade snaps to Anderson who rolls his eyes and does what he's told. Sherlock grunted and went back to thinking and closed his eyes. After a few moments his eyes  
suddenly snap open and takes off. He jumps out of the open window.

"Sherlock!" John exclaims and runs after him. Sam and Dean exchange a glance before leaping out of the window and chase after the Detective and his Blogger.


	2. Accident

"Hey, wait for me!" Lestrade exclaimed before following them. Castiel and Anderson were the only ones left in the house. They stare blankly at each other before Castiel poofs away and Anderson's eyes widen

"WHAT THE HELL?!"

Sherlock sprinted as fast as he could and came to a sudden halt. John skidded to a sudden stop a few seconds behind and nearly crashed into the detective

"There." he whispered pointing to the possessed Kassey. She was in a crouch and sniffed like a blood hound, her eyes were pitch black and sinister. UK was shortly behind John.

"Whoa..." Kassey's head scanned her surroundings like a panther and she locked eyes with Sherlock. Immediately Sherlock sprung into action and tried to catch her. Kassey growled and then jumped onto a nearby brick wall away from Sherlock's arms and hissed to the group below her

"Kassey come on!" UK said. Kassey hisses again, spraying spit everywhere just as Dean, Lestrade, Sam and Castiel arrive

"EW..." UK muttered

Kassey climbs further up the wall, creeping out Lestrade and John further. Sam starts to draw some marking on the ground. Kassey sees what he's doing and uses the air to disrupt the exorcism and push the whole group off their feet

"Jeez…". UK mutters starting to get annoyed. John and Sherlock pick themselves off the ground just as Kassey disappears into the Shadows  
Sherlock curses and the group try to find the girl again. After 5 minutes of looking, The Consulting Detective sighs in frustration

"What's wrong with her?" UK demands and whirls to Sam and Dean

"She's been possessed by a demon." Dean says, his eyes not leaving the spot where Kassey disappeared.

"Will she be ok?"

"If we get it out of her on time"

"What if we don't?" Lestrade asks

"Then the Demon will permanently bond to her body and no matter what kind of exorcism we perform."

"How long do we have?" John asks

"Not that long"

"No more than a week" Castiel says as he pops out of nowhere

"A bit not good." said Sherlock suddenly. Everyone looks to him in surprise

"I'm sorry Sherlock?" John says

"Lost all trace of her"

"OK." John looked to Dean "Where should we start looking?" Sherlock shrugged and pointed to the direction Kassey went

"I'm sorry but can I just ask what the HELL is going on?" Lestrade said

"No." said everyone at the same time

"OK." Lestrade sighed and ran a hand through his grey hair

"Let's go" said Sherlock and everyone started jogging again. They all follow Sherlock down another narrow alley just as a scream pierced the air

"What was that...?" gasped Lestrade

"It would appear to have been a scream. This way!" Sherlock runs to where the scream came from.

And onto the road. It appears to have been a trap. One that Sherlock stepped right into.

"Sherlock! Look Out!" John shouts

Before Sherlock could react, a car impacts with him and quickly drives away.


	3. Saying Hello

"Oh Dear God!" John sprinted to the unmoving detective and kneeled by him. "Oh please be alive… please be alive… Please, please, please…" John put 2 fingers to Sherlock's neck as Lestrade, Castiel, Dean and Sam come over.  
John searched desperately for a pulse. None. Maybe he was doing it wrong? He tried again. No such luck.

"No, no, no, no, no..." Lestrade grew pale as John began to do CPR.

"Come on Sherlock, dammit!" tears were forming in John's eyes. "Come on you selfish bastard!"  
When nothing happened, Lestrade placed a hand on John's shoulder causing the Army Doctor to stop and cover his eyes. Sam, Dean, Castiel and UK stood there awkwardly. Castiel crouched next to the body.

"I can help." he said. John looked to Castiel; his eyes were puffy and red.

"How?" he whispered. Castiel held an arm over Sherlock's heart and closed his eyes.  
After a few moments, Sherlock sat bolt upright and took a deep breath.

"Sherlock!" John exclaimed and pulled Sherlock into a ferocious hug. The Detective looked confused and patted John's back awkwardly

"What just happened?" Sherlock rasped

"You were hit by a car and died." Castiel said

"How the heck did you do that?!" Lestrade breathes. Sherlock inspects his body which was otherwise unharmed

"I am an angel of the lord." replied Castiel. John opened his mouth to speak

"Long story." Dean interrupted

"John... Please let go you are choking me..." gasped Sherlock as pain erupted in his abdomen and as he tried to take air into his lungs

"Sorry!" John pulled away and blushed "I- I just thought you were dead…"

"Apology accepted." Sherlock rasped as he stood "Thank you Castiel."

"You are Welcome."

Lestrade was looking at Sherlock and Cas like they had just done something insane. Well, they had...

Sherlock swayed on his feet as he tried to stand and the angel caught him as he nearly fell

"Sherlock?!" John exclaimed

"You must not rush yourself" Cas said

"M' fine" Sherlock slurred trying to get back on his feet

"Oi, cheekbones I think you should listen to the Angel" Dean said. John held Sherlock as he nearly fell again. The Detective huffed as he tried to stand again but his legs wouldn't listen to him.

"Perhaps Dean is right." John says to Sherlock

"'E called me cheekbones..." Sherlock frowned but did as Dean said and lowered himself to the floor. The moment he was in contact with the ground he blacked out.

"Shit." muttered John. "Will he be ok?"

"He should be fine. It is just the side effects."

"When will be fine again?"

"In an hour or so. Less if he's lucky-"

"He won't be happy about that."

"Allow me to finish. In some cases they recover in 5 minutes."

"Oh right."

"So then we wait?" Lestrade asked

"We wait." Speaking about it Sherlock groaned and opened his eyes. John looked down to the Detective

"You OK?"

"Yes of course I'm ok." Sherlock snapped standing up  
He straightened up, covered his mouth, and coughed. He looked at his hand and quickly wiped it on his coat. John noticed Sherlock's movement and grabs Sherlock's hand which has small smears of blood

"What is this?" Sherlock yanked his hand from Johns grasp.

"Nothing..."

"No it isn't, Sherlock." John presses on

"Ok, it's a red liquid that flows through the veins." Sherlock sighed, only ending up coughing into his palm again.  
Sherlock doubled over and he starts coughing harder. John and Lestrade steady him  
"Cas what's happening?!" Dean shouts as Castiel regards the situation.

"He seems to be coughing. I don't know why... I thought I healed him."

"Well you didn't do a good Job!" John whacks Sherlock's back and he gasps. The blood that was in Sherlock's lungs is spat onto the ground. The consulting detective stands there, still doubled over blood dripping from his lips.

"Sherlock!" John exclaims as blood smears across the gravel. Castiel inspects Sherlock closely, unsure what went wrong. Sherlock took in a deep shaky breath and wiped an arm across his face before trying to stand upright again. John felt the Consulting Detective lean on him heavily

"I think I found out what I did wrong!" Cas shouts and places a hand on Sherlock's chest. After a few moments, he pulls away, satisfied and Sherlock starts breathing normally  
"What did you do?" John asks as Sherlock straightens. Cas rubs the back of his neck sheepishly

"I forgot to heal his fractured ribs and one that pierced his lung..." Sherlock glares at Cas.

"Wow. Exceptional healing there" he mutters and rolls his eyes. Cas looks to Dean in confusion

"Sarcasm." He says and Cas makes an 'oh' face. John looks at Sherlock.

"Are you ok now?"

"I'm fine." Sherlock rasps, his voice hoarse however he is otherwise unharmed  
"Good great, fantastic. Now can we go and save Kassey now?!" UK growls Everyone looks to UK in surprise before they all look away.

"Yes… Ahem, of course" Sherlock says "Does anyone have any idea where she went?"  
"No that was your job." UK mutters. "But... I guess we could go in the general direction she went and hope she ran through some substances that will like a trail like mud..."

Kassey watched from the shadows as the group walk off. She hisses in distaste as she realises the one known as _Sherlock_ begins to walk after his _accident_. She chuckles how much she wanted to see him die. His guts and intestines splattered across the road while blood is smeared across the walls and on his _friends_. She crawls away into the shadows, muttering

"_They will die, they will all die…_"

UK turned around to face the looming shadows of the trees. She could have sworn she herd something. She shrugged after a moment and passed it off as the wind and pulled the sleeves of her hoodie over her hands and pulls her hood up. Sherlock shivered and rubbed his arms through his coat, John looked at him with concern

"You alright?"

"I'm fine…" Sherlock lied and John shook his head.

"Don't you bloody lie to me."

"Nothing ever gets past you does it?" Sherlock smiles

"Oi, quite flirting you two" Lestrade snaps

"Get a room!" Dean shouts causing Sherlock and John turn away from each other.  
"Not gay!" said John with anger. Heat rose to both Sherlock and John's cheeks and John bit his lip.

"I'll believe that when Cas learns how to be human." Dean mocked. John grabbed Sherlock's collar so he could whisper in Sherlock's ear

"What's bothering you?" he asked gently

"I…" Sherlock hesitated "I think we're being watched." In the background Dean wolf whistled

"Ah…" John whispered ignoring Dean. "How do you know?"

"I just have a _feeling_"

"Ok." John nodded and Sherlock pulled away, looking around for any signs or clues. Lestrade looks to the pair curiously

"What's wrong?" Lestrade paused and narrowed his eyes. The bushes rustled and out stepped a stray cat, not a possessed teen. Sherlock frowned and Lestrade laughed.

"Is that what you were so worked up about?" Sherlock shook his head and then shrugged

Kassey crawled through an open window leading to a study which was occupied by a tall man. He whirled as he heard something before staring at Kassey in surprise

"Hello Moriarty." she said


	4. Let's Begin

"Who are you?" James Moriarty asked, intrigued by this black eyed girl that had just crawled through the window. He walked in a circle around her, his trade mark smile dancing across his lips.

"My name is Kassey and I'm going to make you an offer even _you_ wouldn't be able to refuse."

**

Sherlock rubbed the back of his neck. Castiel was bent over and stroking the cat. The cat purred in content and lent into the Angel's hand.

"Oooh so scary!" Dean declared in mock horror, gesturing to the cat and looking at Sherlock smugly. As if saying: Wow, some detective.  
Sherlock didn't notice though.

"No… It wasn't the cat..." He looked around but saw nothing, he sighed

"Let's keep looking." Dean rolled his eyes and turned back to Castiel.  
"Come on. Leave the cat alone" Castiel pouted

"But I wanted to keep it" Dean clasps a hand to his head.

"Well, you can't"

"Please?" Castiel begs with puppy eyes which looked a bit weird on a grown man

"NO!" UK, Sherlock, John, Lestrade, Sam and Dean shout in unison. The cat in question shrikes at the sudden noise and runs off, puffed up.

"Aw… No you scared the cat away..."

"Good. Let's go before it comes back" Dean muttered

The group spent the rest of the night scouring the streets of London until the sun rose to its Highest

**

Moriarty narrowed his eyes

"Why should I trust you?" he asked

"We both have something in common"

"What's that?"

"We're both on the side of the devil"

**

John leaned on an alley wall in exhaustion and rubbed the sleep from his eyes  
Sherlock was the only one who was still alert as ever.

**  
"Oh really?" cooed Moriarty. "And how do you know this?"

Kassey smirked and she splayed her hand causing Moriarty to go flying into a wall. She disappeared and reappeared in front of the suspended Criminal who smirked  
"Proof enough?" Kassey hissed

"I'm all ears."

**  
"Sherlock I think we need a break!" Lestrade sighed and sagged against the wall next to the half-awake John. Sherlock stopped and rolled his eyes.

"Fine. Rest." Besides, it was better to have an alert team opposed to one dead on their feet.

"I think we should head back to the flat." John slurs

"Agreed." Lestrade says and Sherlock nodded.

"But, Kassey-" UK protested

"Can wait."  
UK gave up. She wasn't going to convince them

**

"I can help you with your Consulting Detective problem" Demon Kassey purred and Moriarty chuckled

"Then what's on it for you?"

"I want to drag his soul to hell." Moriarty blinked a few times. Had he just heard this teen correctly?

Without a second thought he held out a hand.

"Deal."

**  
The group arrived back at 221b Baker Street and collapsed onto the many chairs while the ever- helpful Mrs Hudson made tea for everyone with the promise that it was just this once.  
Mrs Hudson came in with tea and coffee and placed the numerous cups on the table.  
Everyone took their drinks gratefully

"So, any information?" UK asked and Sherlock sipped on his tea

"Well, your friend is definitely -as you 3 put it- _possessed_" John looks at Sherlock in disbelief.

"You cannot possibly believe that! You of all people! It's not possible!"  
"But what else can it be!" Sherlock shot back "It was possible that she could have worn black contacts and had some way to climb up a wall, but what would that achieve?! She put her own best friend at risk!" John paused.

"Well, yes, I could be possible that she put in black contacts and it is possible to climb up walls, only in certain conditions though..."

"Fine. Ok. Possessed... But it just seems so unreal!"

"That is where our new guests come in." Sherlock turned to Dean, Sam and Castiel "Just _who_ are you?" Dean and Sam exchange a glance and nod.

"Sam and Dean Winchester. We are hunters." Said Sam.

"That I had already perceived." Sherlock rotated his palm in a 'go on' movement

"We hunt anything supernatural, say, vampires, werewolves, demons etc." Lestrade frowns as the 2 brothers explain

"Vampires? Werewolves?" he questions

"Yep." Sam confirms. "They are real. Everything is real." Lestrade stays silent for a few moments, thinking.

"I'd try not to over-work that brain of yours Lestrade" Sherlock comments. Lestrade rolls his eyes.

"I'm not as dim as you believe, Sherlock."

"Don't lie, yes you are." Lestrade sighs, not bothering to argue anymore

"So you're saying a demon has taken control of Kassey and is using her as a puppet to do its evil?" UK asked Sam and Dean trying to get the squabbling children-adults to shut up.

"Generally, yes" Sam replies

"And we only have a week to get it out of her before it permanently bonds to her body?"  
"Yes." A shiver ran down UK's spine. Great. Just great. With the way everything was going they were not going to get her in time…

"We'll get to her before the week is over." John said reassuringly to UK "Just you wait."

**

"I never thought I would have a truce with a 13 year old _girl_ " Moriarty smiled "I like it."

"Now then," Kassey grins "Shall we Begin?"


End file.
